The comparative pathogenesis of selected bunyaviruses and their RNA segment reassortment (reassortant) progeny viruses will be studied in mosquito vectors. Organ tropisms of reassortant and parental viruses will be determined by in site localization of viral antigen in cryostat sections and organ dissections of infected mosquitoes. In addition, the efficiencies of infection and rates of oral, transovarial, and venereal transmission will be determined for parental and reassortant viruses. This information will be used to determine the contribution of each of the RNA segments to the biological differences seen. Potential for reassortant formation in mosquitoes will also be studied. Virus present in materials collected from mosquitoes transovarially-infected with one virus and subsequently infected via engorgement with a second bunyavirus will be analyzed to determine if reassortants can be generated.